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RE: st: FW: Marginal effects for the two-part model

From   Maarten buis <>
Subject   RE: st: FW: Marginal effects for the two-part model
Date   Tue, 1 Feb 2011 07:58:54 +0000 (GMT)

--- On Tue, 1/2/11, Michael Palmer wrote:
> The first part of the model is logit model for seeking
> hospital care followed by an ols model for the cost of
> care for persons that sought care. 
> Simplified code is: 
> Logit care $xvar, robust
> Reg cost $xvar if care==1
> I am wanting to compute the conditional marginal effects
> but do not know how to do this. 

In this model the cost is independent of seeking care, so
the marginal effects of $xvar on the cost conditional on seeking
care are just your regression coefficients (the output you 
got from -regress-).

Typically, when estimating both parts you would want to 
allow for correlation in the error terms across your two
steps. I tend to think of those correlations as variables
that influence both the probability of seeking care and the
cost and are not in $xvar. If that is what you want, then
you can take a look at -help heckman-.

Hope this helps,

Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen


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